1. Field of the Invention
This invention relates to a hydrophilic porous material sterilizable with .gamma.-rays. More particularly, it relates to a .gamma.-ray-sterilizable hydrophilic porous material which is used for various purposes in the medical field such as purification of blood and separation of blood plasma.
2. Description of the Prior Art
In the application of medial materials to living bodies, sterility is an extremely important consideration as well as safety and bioadaptability. Since clinical use of microorganically contaminated medical materials and medical tools has the possibility that the microorganisms will incite such adverse side effects as fever and infection or diseases, medical materials and medical tools which are incapable of tolerating thorough sterilization are totally worthless no matter how excellent their functions may be.
Heretofore, it has been customary to effect sterilization of medical materials of porous substances by the use of an autoclave or by exposure to ethylene oxide gas. The method of sterilization by the use of an autoclave is complicated operationally and is incapable of sterilizing such medical materials in a large amount at one time. The method of sterilization with ethylene oxide gas entails the problem of residual ethylene oxide gas. On the other hand, the feasibility of a method of sterilization with .gamma.-rays which is simple in operation and free from worry concerning any remnant of used sterilizer has been studied as regards.
When conventional porous materials are sterilized by exposure to .gamma.-rays, the polymer substances forming the porous materials are deteriorated. Consequently, the porous materials lose strength possibly causing inconvenient handling due to the susceptibility of such porous materials to damage or leakage in the course of module assembly and a susceptibility of the materials to loss of resistance to pressure in the course of actual service. Polypropylene type porous materials, for example, are excellent in such properties as chemical resistance, dimensional stability, and mechanical strength and, therefore, are expected to find extensive utility in various medical applications. Since polypropylene rather easily succumbs to cleavage of the main chain and a cross-linking reaction on exposure to .gamma.-rays, however, application of the method of sterilization with .gamma.-rays mentioned should be further studied.
The porous materials made of hydrophobic polymer substances represented by such polypropylene type porous materials as described above indeed excel in such properties as chemical resistance, dimensional stability, and mechanical strength but nevertheless must undergo a treatment to impart hydrophilicity such as by alcohol-water displacement, before the materials are put to use for the treatment of aqueous media. The impartation of hydrophilicity proves to be extremely complicated operationally. Various methods, therefore, have been heretofore proposed for modifying porous materials made of hydrophobic polymer substances, such as by coating their surfaces with such hydrophilic materials as surfactant, polyethylene glycol, and polyvinyl alcohol and cross-linking and insolubilizing them with polymers formed mainly of such hydrophilic monomers as N,N-dimethyl acrylamide, 2-hydroxyethyl methacrylate, and N-vinyl pyrrolidone. The porous materials which have hydrophilicity imparted thereto by these methods, however, are invariably found to induce exudation as a consequence of exposure to .gamma.-rays. Use of these porous materials in medical materials, therefore, may not be safe.
An object of this invention, therefore, is to provide a novel hydrophilic porous material sterilizable with .gamma.-rays.
Another object of this invention is to provide a .gamma.-ray-sterilizable hydrophilic porous material which is used favorably in the medical field for such purpose as purification of blood and separation of blood plasma.
The further object of this invention is to provide a .gamma.-ray-sterilizable hydrophilic porous material which retains practical bursting elongation even after exposure to .gamma.-rays, yields to exudation only sparingly, and ensures high safety.